Briefing Chat: An invisible tattoo that appears under UV light – and then disappears

Benjamin Thompson (0:04)

Hi, listeners, Benjamin here. It's the Friday show, The Briefing Chat, where we talk about a couple of stories that have been covered in The Nature Briefing. Joining me this week is Maren Hunsberger. Maren, how are you doing?

Maren Hunsberger (0:13)

Hello, I'm great. Happy to be here, as always.

Benjamin Thompson (0:15)

Excellent. Well, listen, why don't you go first this week? You've got an interesting story about ink.

Maren Hunsberger (0:19)

I do, and I'm going to open with a question for you, Ben. Would you get a tattoo if you could turn it on and off?

Benjamin Thompson (0:26)

Sure. I mean, yeah.

Maren Hunsberger (0:27)

I think maybe some people would, even if they hadn't considered getting a normal tattoo, this kind, they might.

This kind of tattoo is made out of something called a photochromic dye. And you might be familiar with this because we have photochromic materials in other places in our lives, like transition lenses. So when you go outside, you have glasses on, they darken. That's a photochromic material. It means that it responds to a certain wavelength of light by changing color. Now, what happens here is that when a certain wavelength of light hits that molecule, it changes shape so that it changes color. But what's really cool about it is that when it's exposed to a different wavelength of light, that change reverses. It goes back to its original shape and it disappears.

Benjamin Thompson (1:09)

So you can literally turn it on or off.

Maren Hunsberger (1:11)

Exactly. And so we have these materials in other places in our lives. Like I mentioned, these transition lenses is a great example. This paper that came out in the cell last week is the first evidence that we have of a photochromic material that has been injected into living human skin.

Benjamin Thompson (1:26)

Right. Now, I've seen a thing about UV tattoos, which shine when under a black light. Is this similar to that?

Maren Hunsberger (1:33)

Exactly. So anybody who's familiar with the rave scene is probably familiar with UV tattoos that, as Ben says, glow under black light. It's similar in a sense, but they're actually quite unique. So UV tattoo is a tattoo that's been done with fluorescent dye. So its molecule is excited by a certain wavelength of photon, and it only glows when a black light is shining on it. What's different about these photochromic dye tattoos is that they are activated by a certain wavelength of UV light, and then they stay on.

Benjamin Thompson (2:03)

So sort of semi-permanent.

Maren Hunsberger (2:05)

Exactly, until you can turn them off by exposing them to very strong, visible light.

Benjamin Thompson (2:10)

And you say that this has been tried in a human. Was this in a warehouse with sort of pumping techno? What was the situation here?

Maren Hunsberger (2:15)

So this brings us to a great line from the paper. In the abstract, it says, In a single subject in Vivo Pilot, all three channels, this is the three colors of photochromic dye, remain fully photo switchable, rewritable, and selectively erasable in healed human skin after more than two years. Have a guess, Ben, about who that single subject is.

Benjamin Thompson (2:38)

So I knew a tattoo artist who used to test things out on himself, right? To show customers how the inks would fade over time. I'm getting a sense that testing tattoo stuff out on yourself is probably involved here in some case.

Maren Hunsberger (2:52)

Yes, you are correct. The person in question is the lead researcher on this story. He is a nanomaterials guy and he has founded this startup that is called Hyperskin that specializes in these more alternative nanomaterial tattoo methods. And what's interesting is that it's not only helpful for cosmetic or artistic purposes, right? So there are some great videos on our site that listeners can go check out of the researcher highlighting the tattoo or even, you know, there's an instance where you can inject basically an entire canvas of this ink. And then you have this device that looks like a pen with a UV light in the tip and you can write on your skin and the dye shows up in this shape of what you've written. It's kind of amazing. But outside of, you know, maybe wanting to erase your tattoos when you're around your family, even though you're fond of them, this could be really applicable for medical applications. So when folks have to get a tattoo for radiotherapy or to indicate where they've gotten a biopsy, some folks really don't like to have that reminder. They don't like to have that staring at them all the time. So you could do them with an ink like this instead.